Methods of rejuvenating sputtering targets

ABSTRACT

In various embodiments, a sputtering target initially formed by ingot metallurgy or powder metallurgy and comprising a sputtering-target material is provided, the sputtering-target material (i) comprising a refractory metal, (ii) defining a recessed furrow therein, and (iii) having a first grain size and a first crystalline microstructure. A powder is spray-deposited within the furrow to form a layer therein, the layer (i) comprising the metal, (ii) having a second grain size finer than the first grain size, and (iii) having a second crystalline microstructure more random than the first crystalline microstructure. Spray-depositing the powder within the furrow forms a distinct boundary line between the layer and the sputtering-target material.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/937,164, filed on Nov. 8, 2007, now U.S. Pat. No. 8,197,894, whichclaims priority to and the benefit of U.S. Provisional PatentApplication No. 60/915,967, filed on May 4, 2007. The entire content ofeach of these applications is incorporated by reference herein.

BACKGROUND

It is well known in the art that the physical properties of sputteringtargets employed for Physical Vapor Deposition (PVD) in the electronicsindustry greatly influence the final properties of the thin filmsproduced. In fact the target properties that enable and enhance themanufacture of high quality thin film devices and circuitry are:

Fine and uniformly fine grain structure.

Random and uniformly random crystallographic orientation of theindividual grains.

A microstructure that when viewed on the macroscale is substantiallyinvariant throughout the entire body of the target.

A microstructure that can be repeated from target to target.

A microstructure that is substantially 100% dense and provides highstrength intergranular bonding.

These properties are in particular very difficult to attain in tantalum(Ta) and niobium (Nb) targets. This results from the fact that highpurity Ta and Nb are refined and purified via electron beam melting andcasting into a cold, water cooled mold. The ingot formed has manyextremely large grains measured in multiples of centimeters in bothwidth and length. These extremely large grains require extensive andexpensive thermomechanical processing in order to reduce the grain sizeand reduce the crystallographic alignment of the individual grains(reduce the texture). Thermomechanical processing has limits in thereduction in grain size, crystallographic randomness produced, and theuniformity of microstructure produced. Typically tantalum targetmaterial produced from ingot still contains a large degree ofnonuniformity described as grain size and texture banding-regions wherethere is a common grain size and texture that is not typical of theoverall grain size and texture of the entire target.

The importance and magnitude of this problem was addressed in U.S. Pat.No. 6,193,821 where ingots were first side forged or side rolledfollowed by upset forging or upset rolling. U.S. Patent Publication No.2002/0112789 A1 describes a process utilizing upset forging followed bydraw back forging then side forging and finally a cross rolling processto provide a mix of grains with the {100} and {111} orientation. In U.S.Pat. Nos. 6,331,233 and 7,101,447 the inventor specified a complex threestep process consisting of multiple deformation and annealingcomponents. But while the complex processing route successfully refinedgrain size the processing still resulted in a predominantly {111}texture.

US Patent Publication No. 2005/0155856 A1 describes a Ta sputteringtarget which has a preferential (222) orientation over a limited portionof the target thickness which it is claimed improves the uniformity ofthe sputtered film thickness.

Other patents recognize the inherent advantages of starting withtantalum metal powder rather than a solid tantalum ingot. U.S. Pat. Nos.5,580,516 and 6,521,173 describes cold compact Ta powder into billetsthat then may undergo a wide range of thermal/mechanical processtechniques in order to produce fully dense billets from which sputteringtargets can be made. U.S. Pat. No. 6,770,154 describes consolidating apowder billet to full density followed by rolling and annealing toprovide a uniform but not random grain structure. U.S. Pat. No.7,081,148 expands upon the processes of U.S. Pat. No. 6,770,154 toinclude a resultant tantalum sputtering target that is at least 99.99%pure tantalum.

U.S. Pat. No. 7,067,197 describes a powder metallurgy process that firstsurface nitrides the tantalum powder before compaction. The surfacenitride powder may then be compacted by a list of at least 23 differentprocessing steps that must retain the high nitrogen content of thepowder. One of the least favorable is spray depositing, although nomention of what type of spray deposition technology is being used i.e.plasma spray, low pressure plasma deposition, flame spray, high velocityoxyfuel, etc. a few of the many processes currently employed.

WO 2006/117145 and WO 2006/117144 describe cold spray processes forproducing coatings of tantalum.

The rejuvenation or reprocessing or repair of used targets is also ofeconomical interest due to the fact that tantalum and the processes forbonding tantalum to backing plates are quite expensive. This iscompounded by the fact that only about 25-30% of a planar target and60-70% of a rotary target is used in sputtering before the entire targetmust be replaced. Thus the recovery of the unused Ta is of muchinterest.

U.S. Patent Publication No. 2004/0065546 A1 discloses a method ofhydriding the tantalum target so that the tantalum is embrittledallowing it to be separated from the backing plate, ground up, andreused as a powder stock in making ingots. U.S. Patent Publication No.2006/0032735 discusses the use of laser beams and other focused energysources in order to simultaneously melt and fuse powder that is fed intothe worn areas of a used target in order to fill the void created by thesputtering. Of course all these techniques generate substantial heat andrequire the backing plate be removed from the target prior to repair.Additionally, as is well known to one of ordinary skill in the art, whenmelting occurs the powders resolidify by directional manner and theresulting microstructure has strong textural components.

Before a target can be used it must be machined to final dimensions andthen soldered, brazed or diffusion bonded to a high thermal conductivitybacking plate for mounting in the sputtering machine.

Sputtering targets are used to make a wide range of thin films withapplications ranging from reflective and low emissivity coatings forwindow glass (Nb), photovoltaic films (Mo), narrow pass filters (TaNb)etc. Perhaps their best known use however is in integrated circuitrywhere layered sputtered films are used to make the basic switchingdevices as well as the circuitry to connect them producing functionalelectronic components (integrated circuits, flat panel displays, etc.).As stated above the quality of the thin films made and hence the qualityof the products made using thin film technology, are highly dependent onthe quality of the target they are sputtered from.

Cold spray or kinetic spray (see U.S. Pat. Nos. 5,302,414, 6,502,767 and6,759,085; Van Steenkiste et al, “Analysis of Tantalum Coatings Producedby the Kinetic Spray Process” Journal of Thermal Spray Technology, Vol.13 (2) June 2004 pages 265-273, U.S. Pat. No. 6,139,913, and U.S.Publication Nos. 20050120957 and 20050252450) is an emerging industrialtechnology that is being employed to solve many industrial manufacturingchallenges (see, also e.g., U.S. Pat. Nos. 6,924,974; 6,444,259;6,491,208 and 6,905,728).

Cold spray employs a high velocity gas jet to rapidly acceleratepowders, typically less than approximately 44 microns in size, to highvelocity such that when they impact a surface the powders bond to thesurface to form an integral, well bonded and dense coating. The coldspraying of tantalum powders onto a variety of substrates (includingsteel) has been suggested (see, e.g., “Analysis of Tantalum CoatingsProduced by the Kinetic Spray Process,” Van Steenkiste et al, Journal ofThermal Spray Technology, volume 13, number 2, June 2004, pages 265-273;“Cold spraying—innovative layers for new applications,” Marx et al,Journal of Thermal Spray Technology, volume 15, number 2, June 2006,pages 177-183; and “The Cold Spray Process and Its Potential forIndustrial Applications,” Gartner et al, Journal of Thermal SprayTechnology, volume 15, number 2, June 2006, pages 223-232). This is allaccomplished without having to heat the powder to a temperature near orabove its melting point as is done with traditional thermal sprayprocesses. The fact that dense coatings can be formed at lowtemperatures present many advantages. Such advantages include lack ofoxidation, high density deposits, solid state compaction, the lack ofthermally induced stresses and particularly, in this case, the lack ofsubstantial substrate heating.

Kinetic spray can be accomplished for example, by injecting Ta startingpowders having particle diameters great than 65 μm into a de Laval-typenozzle, entrained in a supersonic gas stream and accelerated to highvelocities due to drag effects. The particle's kinetic energy istransformed via plastic deformation into strain and heat on impact withthe substrate surface. The particles are melted in the process.

Limited substrate heating is preferred in the instance of manufacturingcathode or electronic sputtering target blanks for the field of PhysicalVapor Deposition (PVD). Target materials are frequently high meltingtemperature (“TM”) refractory metals (Ta TM=2998 C) while the backingplate that supports the target is chosen for its high thermalconductivity and is typically copper or aluminum (Al TM=660 C), both lowmelting temperature materials. Thus other thermal spray processes thatrequire heating of the powder to at or near its melting point can not beused to deposit refractory metals on the low melting temperature backingplate. Current practice is to make the target completely separate fromthe backing plate and then use solder, brazing, diffusion bonding orexplosive bonding techniques in order to bond the target and backingplate together. Because cold or kinetic spray does not substantiallyheat the powder it can be used to make targets directly on the backingplate as well as repair used targets without the need of having toremove the target from the backing plate.

A BRIEF SUMMARY OF THE INVENTION

It is an object of the invention to manufacture a sputtering target thathas a uniformly fine and crystallographically random microstructurethroughout the entire body of the target.

It is a further object of the invention to provide a manufacturingprocess that can cost effectively create such a microstructure, andrepeat that structure from target to target. Preferably, the processdoes not require melting. Examples of such processes include cold sprayor kinetic spray processes.

It is a further object of the invention to provide a cost effectiverepair or rejuvenation process that gives the repaired target the sameor better microstructure as it originally had.

It is a further object to develop a target rejuvenation process by amethod that does not require melting such as cold spray or kineticspray.

We have discovered a technique and parameters that allow directfabrication of targets with a fine, randomly oriented grain structure,through the entire thickness of the target without the complexprocessing described above, a technique that allows the manufacture oftargets directly on the backing plate with the desired microstructureand for used targets to be repaired simply. That technique does not usea melting process. Examples of such processes include cold spray orkinetic spraying of fine metal powders such as, but not limited totantalum powder.

Additionally, the present invention provides a method of sputtering,whereby any of the above-described sputtering targets are subjected tosputtering conditions and are thereby sputtered. Any suitable sputteringmethod can be used in the present invention. Suitable sputtering methodsinclude, but are not limited to, magnetron sputtering, pulse lasersputtering, ion beam sputtering, triode sputtering, and combinationsthereof.

Additionally, the present invention provides a sputtering target whichcomprises a fine uniform grain structure of essentially less than 44microns, that has no preferred texture orientation (i.e. consistsessentially of randomly orientated grains) as measured by electron backscattered diffraction (“EBSD”), consists essentially of less than 44micron grains, and that displays no grain size or texture bandingthroughout the body of the target.

Additionally, the present invention provides a target which comprises anequiaxed grain size in annealed state, grain size smaller than startingpowder particle size.

Additionally, the present invention provides a sputtering target with alenticular grain structure characterized by substantially nointerparticle diffusion that has no preferred texture orientation asmeasured by EBSD and that displays no grain size or texture bandingthroughout the body of the target.

Additionally, the present invention provides a process for manufacturinga sputtering target assembly in an additive manner by depositing thetarget materials via a powder spray directly upon the backing plate usedin the target assembly, machining of that deposit and substrate to finaltarget assembly dimensions in a single step.

The present invention also provides a method of making a thin filmincluding the steps of:

(a) sputtering the above-described sputtering target;

(b) removing metal atoms from the target; and

(c) forming a thin film comprising the above metal onto a substrate.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates flat planar tantalum targets made by cold sprayingusing nitrogen gas and helium gas.

FIG. 2 illustrates flat planar tantalum targets made by cold sprayingafter sputtering.

FIG. 3 illustrates scanning electron microscope (“SEM”) micrographs ofsputtered tantalum thin films from targets prepared by helium coldspray, nitrogen cold spray and rolled billet.

FIG. 4A illustrates close ups of rolled target after sputteringrevealing mottled and irregular surface of the rolled target.

FIG. 4B illustrates close ups of helium cold sprayed target aftersputtering revealing smoother, non mottled surface of the cold spraytarget.

FIG. 5 illustrates tantalum tubular performs according to the invention.

FIG. 6 illustrates micrographs of as sprayed and annealed structurestaken normal to the direction of spray.

FIGS. 7A and B illustrate results using cold spray and annealed at 1450C.

FIG. 8 illustrates results using cold spray and annealed at 1150 C.

FIG. 9 illustrates results using cold spray and annealed at 942 C.

FIG. 10 illustrates the base-plate had equiaxed, very large, grains,with a texture typical of rolled and over annealed plate.

FIG. 11 illustrates pole figures according to the invention.

FIG. 12 illustrates the Plasma-sprayed tantalum sample having equiaxed,very large grains with a texture typical of rolled and over-annealedplate.

FIG. 13 illustrates pole figures according to the invention.

FIG. 14 illustrates, cold Sprayed TaNb target. Deposit is over 440 mmlong, 110 mm wide and 7 mm thick. Note 3 mm bow induced at center of thecopper backing plate.

FIG. 15 illustrates Load vs. deflection for as sprayed Tantalum. Notethe deposit fails by brittle fracture, without exhibiting any plasticdeformation.

FIG. 16 illustrates permanent set obtained in Ta deposit after 0.08inches of deflection during bend test.

FIG. 17 illustrates a target after annealing and straightening. Straightedge ruler demonstrates the bow has been successfully removed.

FIG. 18 illustrates a schematic view for TFT-LCD.

FIG. 19 illustrates an example of a hard disk drive.

FIG. 20 illustrates a schematic of an inductive read/write head and aGMR read head.

FIG. 21 illustrates the cross section diagram of a diffusion barrierlayer of a semiconductor device.

FIG. 22 illustrates a printer head according to the invention.

FIG. 23 illustrates the microstructure of a MoTi target and thedeleterious phases and interdiffusion zone produced during hot isostaticpressing (“HIPing”) to consolidate the powder.

FIG. 24 illustrates the microstructure of an as sprayed MoTi targetproduced by cold spray that contains only elemental Mo and elemental Tiand no deleterious phase formation.

FIG. 25 illustrates cold sprayed MoTi after a 700 C 1.5 hour annealshowing that substantially no deleterious phase has been formed comparedto a hot isostatic pressing (“HIPed”) target (FIG. 23).

FIG. 26A illustrates the microstructure of W—Cu (50/50 vol %).

FIG. 26B illustrates Cu that has a flattened structure.

DESCRIPTION OF THE INVENTION

We have discovered a technique and parameters that allow directfabrication of targets without the complex processing described above, atechnique that allow the manufacture of targets directly on the backingplate with the desired microstructure and used targets to be repairedsimply with or without the prior removal of the used target from thebacking plate. That technique does not use a melting process. Examplesof such processes include cold spray or kinetic spraying of fine metalpowders such as, but not limited to tantalum powder.

The technique can also be used for regenerating or the repair of asputtering target.

As the gas with which the metal powder forms a gas-powder mixture thereis generally used an inert gas. Inert gas according to the inventionincludes, but is not limited to argon, helium, or relativelynon-reactive nitrogen or mixtures of two or more thereof. In particularcases, air may also be used. If safety regulations are met, also the useof hydrogen or mixtures of hydrogen with other gases would be consideredand can be used advantageously due to hydrogen's extremely high sonicvelocity. In fact hydrogen's sonic velocity is 30% greater than that ofhelium which in turn is approximately 3 times that of nitrogen. The airsonic velocity is 344 m/s at 20 C and 1 atmosphere (atm), while hydrogenwith molecular weight 2.016 is the lightest element, compared to air'smolecular weight of 28.96. Its density is about 14 times less than airand has a sonic velocity of 1308 m/s.

In one preferred version of the process the spraying comprises the stepsof:

providing a spraying orifice adjacent a surface to be coated byspraying;

providing to the spraying orifice a powder of a particulate materialchosen from the group consisting of niobium, tantalum, tungsten,molybdenum, titanium, zirconium, mixtures of at least two thereof oralloys thereof with one another or other metals, the powder having aparticle size of 0.5 to 150 μm, preferably 5 to 80 μm and mostpreferably 10 to 44 μm said powder being under pressure;

providing an inert gas at an elevated stagnation pressure to thespraying orifice and providing a spray of said particulate material andgas onto a substrate surface to be coated;

locating the spraying orifice in a region of low ambient pressure;

which is substantially less than the stagnation pressure before thespraying orifice to provide substantial acceleration of the spray ofsaid particulate material and gas onto said surface to be coated and

whereby the substrate is coated with a densified coating on said coatingis annealed. It is noted that the densified coating maybe removed fromthe substrate before or after annealing.

In another preferred version of the process the spraying is performedwith a cold spray gun and the target to be coated and the cold spray gunare located within an inerted chamber at pressures below 80 kPa, orabove 0.1 Mpa.

Throughout the application the term cold spray is used. It is understoodthat it is possible to use a kinetic spray process instead of the coldspray process in the instances only a cold spray process is referred to.

In another preferred version of the process the spraying is performedwith a kinetic device. The kinetic process produces coating using largerparticle size distribution between 65 and 200 μm and higher particletemperatures, compared to cold spray process using particle diametersless than 50 μm with higher particle velocities and usually lowerparticle temperatures. Since the kinetic energy is proportional to cubeof particle diameter, and square of particle velocity, the total kineticenergy, available for plastic deformation, is usually greater than thatof cold spray process. The kinetic spray is performed with a longernozzle length after the throat region (such as 280 mm vs standard 80mm), and higher gas temperature (for example higher than 200 C, but muchbelow the material's melting point). The higher particle velocitiesimprove the coating properties resulting in a high degree of plasticdeformation, increased adhesion, lower porosity and higher workhardening compared with coatings produced with shorter nozzle.

In general, the refractory metal has a purity of at least 99%, such as99.5% or 99.7%, 99.9%, advantageously has a purity of at least 99.95%,based on metallic impurities, especially of at least 99.995% or of atleast 99.999%, in particular of at least 99.9995%.

In general if an alloy is used instead of a single refractory metal,then at least the refractory metal, but preferably the alloy as a whole,has that purity, so that a corresponding highly pure coating can beproduced.

In one of the embodiments according to the invention the total contentof non-metallic impurities in powders, such as oxygen, carbon, nitrogenor hydrogen, should advantageously be less than 1,000 ppm, preferablyless than 500 ppm, and more preferably less than 150 ppm.

In one of the embodiments according to the invention, the oxygen contentis 50 ppm or less, the nitrogen content is 25 ppm or less and the carboncontent is 25 ppm or less.

The content of metallic impurities is advantageously 500 ppm or less,preferably 100 ppm or less and most preferably 50 ppm or less, inparticular 10 ppm or less.

Such metal powders can be purchased commercially or can be prepared byreduction of refractory metal compound with a reducing agent andpreferably subsequent deoxidation. Tungsten oxide or molybdenum oxide,for example, is reduced in a stream of hydrogen at elevated temperature.The preparation is described, for example, in Schubert, Lassner,“Tungsten”, Kluwer Academic/Plenum Publishers, New York, 1999 or Brauer,“Handbuch der Praparativen Anorganischen Chemie”, Ferdinand Enke VerlagStuttgart, 1981, p 1530.

In the case of tantalum and niobium, the preparation is in most casescarried out by reducing alkali heptafluoro-tantalates and earth alkalinemetal heptafluoro-tantalates or the oxides, such as, for example, sodiumheptafluorotantalate, potassium heptafluorotantalate, sodiumheptafluoroniobate or potassium heptafluoroniobate, with an alkali oralkaline earth metal. The reduction can be carried out in a salt meltwith the addition of, for example, sodium, or in the gas phase, calciumor magnesium vapor advantageously being used. It is also possible to mixthe refractory metal compound with the alkali or alkaline earth metaland heat the mixture. A hydrogen atmosphere may be advantageous. A largenumber of suitable processes is known to the person skilled in the art,as are process parameters from which suitable reaction conditions can beselected. Suitable processes are described, for example, in U.S. Pat.No. 4,483,819 and WO 98/37249.

If a low oxygen content is desired, a further process for preparing purepowder having a low oxygen content consists in reducing a refractorymetal hydride using an alkaline earth metal as reducing agent, asdisclosed, for example, in WO 01/12364 and EP-A-1200218.

The invention moreover relates to a process for reprocessing of asputter target (source of metal in cathode sputtering of metal), whereina gas flow forms a gas/powder mixture with a powder of a material chosenfrom the group consisting of niobium, tantalum, tungsten, molybdenum,titanium, zirconium or mixtures of two or more thereof or alloys thereofwith at least two thereof or with other metals, the powder has aparticle size of 0.5 to 150 microns, wherein a supersonic speed isimparted to the gas flow and the jet of supersonic speed is directed onto the surface of the object to be reprocessed or produced.

A sputter target is a source of metal in the cathode sputtering ofmetal. These are employed in the production of integrated circuits,semiconductors and other electrical, magnetic and optical products.During the sputtering process, in general the metal surface of thesputter target is worn away non-uniformly, which leads to a furrow onthe surface. To avoid contamination with the material of the backingplate or even a catastrophic breakthrough of cooling liquid, the sputtertargets are not used until the refractory metal target is used up, butare taken out of service promptly beforehand, so that only a relativelysmall amount of the expensive refractory metal is used up when a newsputter target must be employed. The majority can merely be sold asscrap, or their materials recycled, since removal of the backing plateis required and connection to a new refractory metal plate is necessary.The backing plate here, however, is the part of the sputter target whichis of lower value.

There is therefore a need for a technique which either renders possiblereprocessing of or rejuvenating a sputter target without having todetach the backing plate for this or which renders possible to depositthe sputter material direct to the backing plate or for a rotary targetbacking tube.

For this purpose, the furrow in a used sputter target is topped up againwith the particular refractory metal. It is preferably done without theuse of melting. It can be done for example, by the cold spray or kineticprocess, as described above. For this, the jet of supersonic speed ofthe gas/powder mixture is directed on to the furrow and moved over thecomplete length and shape of the furrow. This is repeated as often as isnecessary to top up the furrow again, so that the surface of the sputtertarget forms a substantially flat area again and/or the topped-upmaterial is raised slightly above the surface of the sputter target.Preferably, the jet of supersonic speed of the gas/powder mixture isthen directed on to the remaining surface of the sputter target andguided over the complete length, breadth and shape of the sputter targetsurface until a uniformly thick and flat layer which completely coversthe surface of the sputter target has been obtained. The rough surfaceobtained can then be ground and polished by the conventional processes,so that the desired smooth surface is obtained.

We note that if the original target was made by conventional ingotmetallurgy or powder metallurgy techniques the cold sprayed repair willhave a finer grain size and more random structure than the originaltarget. If the original target were made by cold spray the repair willhave a similar if indistinguishable microstructure from the originaltarget. There will however be a distinct boundary line between theoriginal target and the repaired zone that is visible in cross sectionof the target.

During production of a new sputter target, the target is applieddirectly to a backing plate. Depending upon the construction of thetarget the jet of supersonic speed of the gas/powder mixture istherefore either directed on to the complete surface of the backingplate of the sputter target and guided over the complete length, breadthand shape of the sputter target surface, until a uniformly andsufficiently thick and flat layer which completely covers the surface ofthe sputter target has been obtained or only the contact area of theplasma is coated which results in a considerable saving of material.

Preferred are targets with a thickness between 2 and 20 mm, morepreferred between 3.0 and 15 mm, still more preferred between 5 and 12mm, still more preferred between 8 and 10 mm.

The purities and oxygen contents of the targets obtained should deviatenot more than 5% and preferably not more than 1% from those of thepowder.

This can advantageously be achieved if the sputter target to bereprocessed is coated under an inert gas. Argon is advantageously usedas the inert gas, because of a higher density than air, it tends tocover the object to be coated and to remain present, especially if thesputter target is in a vessel which prevents the argon from escaping orflowing out and argon is topped up continuously. Other inert gases thatwork according to the invention are discussed above.

The process according to the present invention is particularly suitablefor the processing or production of sputtering targets, because on theone hand during production by thermomechanical processescrystallographic preferred orientations which can change at differentintervals often occur, so that no uniform texture is obtained andinstead so-called bands, that is to say regions of different preferredorientations occur. In thermomechanical processes, this can be preventedonly with very complicated and expensive processes. In contrast, auniformly random texture in which there is no detectable preferredorientations present over the thickness of the refractory metal target,may be obtained by the process according to the invention.

A uniform and random particle size distribution and grain sizedistribution is likewise obtained in the targets, so that also no bandsof different particle size or grain size are obtained if this is notdesired. Banding in grain size or texture in sputtering targets isparticularly bad as it results in variations of the sputter rate andfilm uniformity.

In processes in which powder is applied to the sputter target andmelted, experience shows that bubbling and grain growth occurs. Thisalso cannot be observed in the process according to the invention.

After application of the target, the surface of the sputter target isusually ground and polished in order to obtain a suitable smoothsurface. This can be carried out by the conventional processes accordingto the prior art.

In the production of a new sputter target, the target is applied to abacking means, e.g. to a backing plate. This plate is in general a plateof copper or aluminum or an alloy of at least one of these metals withberyllium. This backing plate can contain channels in which there is acooling medium.

The backing plate and therefore also the sputter target can be in theform of a flat, rod, cylinder, block or any other desired shape.Additional structural components liquid cooling coils and/or a largercoolant reservoir and/or complex flanges or other mechanical orelectrical structures can also be attached.

The targets which are fabricated according to the invention, or targetswhich are produced during production or reprocessing of a sputtertarget, can have a high purity and a low oxygen content.

The resultant target has a content of gaseous impurities which deviatesnot more than 50%, or not more than 20%, or not more than 10%, or notmore than 5%, or not more than 1% from the content of the startingpowder with which this target has been produced. In this context, theterm deviation is to be understood as meaning, in particular, anincrease; the targets obtained should thus advantageously have a contentof gaseous impurities which is not more than 50% above the content ofthe starting powder.

The powder densified on the surface preferably has an oxygen contentwhich deviates not more than 5%, in particular not more than 1% from theoxygen content of the starting powder.

In an advantageous embodiment, the targets moreover have a density of atleast 97%, preferably greater than 98%, in particular greater than 99%or 99.5%. The density of the target here is a measure of the closednature and porosity of the target. 97% density of a target means thatthe target has a density of 97% of the bulk material. A closed,substantially pore-free target always has a density of more than 99.5%.The density can be determined either by image analysis of across-section image (cross-section) of such a target, or by heliumpyknometry. The latter method is preferred less, since in the case ofvery dense targets, pores present in targets further-removed from thesurface are not detected and a lower porosity than is actually presentis therefore measured. The density can be determined by image analysisby first determining the total area of the target to be investigated inthe image section of the microscope, and then relating this area to theareas of the pores. Pores which are far-removed from the surface andclose to the interface to the substrate are also recorded by this means.A high density of at least 97%, preferably greater than 98%, inparticular greater than 99% or 99.5% is important in particular in theproduction or reprocessing of sputter targets.

The targets show high mechanical strength which is caused by their highdensity and by the high deformation of the particles, in the case oftantalum, the strengths are therefore at least 80 MPa, more preferablyat least 100 MPa, most preferably at least 140 MPa if nitrogen is thegas with which the metal powder forms a gas/powder mixture. Thismechanical strength and ductility of the sprayed powder can be furtherincreased by providing an annealing or diffusion bonding heat treatmentafter spraying.

If helium is used, the strength usually is at least 150 MPa, preferablyat least 170 MPa, most preferably at least 200 MPa and very mostpreferred greater than 250 MPa.

The present invention also provides a method of making a thin filmincluding the steps of:

(a) Making the desired sputtering target by cold spray or kinetic spray

(b) sputtering the above-described sputtering target;

(c) removing metal atoms from the target; and

(d) forming a thin film comprising metal atoms onto a substrate.

The metal atoms according to the invention include, but are not limitedto niobium, tantalum, tungsten, molybdenum, titanium, zirconium,chromium, vanadium, magnesium, tin, lead, aluminum, zinc, copper,rhodium, silver, gold, cobalt, iron, ruthenium, rhenium, gallium,indium, antimony, mixtures of two or more thereof or alloys of two ormore thereof or alloys with other metals which have the above-mentionedproperties. Depending on the application of the thin film would dictatewhich metal or combination of metal atoms are used in making thesputtering target.

In another embodiment of the invention, after (c), a step can be addedwhich includes supplying a reactive gas to the metal atoms. A reactivegas is a gas that includes a component that can react with the metalatoms either in a gaseous state or once deposited onto a substrate toform a metal or alloy compound. As a non-limiting example, the reactivegas can be oxygen, nitrogen and/or a silicon containing gas.

The thin film applied by the present method can have any desiredthickness. The thickness of the thin film will depend on the end useapplication desired. Typically, the thickness of the thin film can be atleast 0.5 nm, in some situations at least 1 nm, in some cases at least 5nm, in other cases at least 10 nm, in some situations at least 25 nm, inother situations at least 50 nm, in some circumstance at least 75 nm andin other circumstances at least 100 nm. Also, the film thickness can beup to 10 μm, in some cases up to 5 μm, in other cases up to 2 μm, insome situations up to 1 μm and in other situations up to 0.5 μm. Thefilm thickness can be any of the stated values or can range between anyof the values stated above. The advantage of the thin film according tothe invention is that the thin film can have an excellent uniformity andvery small surface roughness. Surprisingly, under similar magnetronsputtering conditions, the thin film's non-uniformity made fromcold-sprayed tantalum target ranges from 1.5%-4%, compared to 4.3%-15.4%film non-uniformity made from conventional ingot-rolled tantalum target(as shown in Table 1). The improved thin film uniformity is the resultof cold spray target exhibiting features of randomly uniform texture andfine grain size substantially smaller than 44 μm.

The use of the thin film according to the invention encompasses productsused in various applications. In one embodiment, a thin film made inaccordance with the invention can be used in thin film transistor(TFT)-liquid crystal display (LCD) applications. Also, in anotherembodiment, the invention encompasses a thin film used in solar cellapplications, sensor applications, semiconductor devices and metal gatesfor CMOS technology (complementary metal oxide semiconductor). In oneembodiment, the invention is directed to a TFT-LCD device containingmolybdenum thin films that serve as gate electrodes that have excellentuniformity. Another embodiment is directed to thin film solar cellapplications, where the invention encompasses solar cells in which Mothin films function as a back contact as well as barrier layer. The thinfilm can be used in ink-jet printing head application (for example,tantalum is used as a heating element (a highly corrosion resistantmetal material), a cavitation barrier, and a passivation layer (asTa₂O₅) providing a higher electric breakdown), or architectural glasscoatings, the thin film can be or be part of a flat panel display, or amagnetic thin film material as disk-drive storage, and optical coatings.The thin film according to the invention can replace the conventionalthin film according to the prior art.

Due to the uniformity of grain size and texture through the thickness ofthe metal sputtering targets, the films obtained from such targets haveexcellent uniformity, as the cold-sprayed target is “fine-grained,non-banded with random grain orientation.

Solar cell devices are well known in the art. For example, the followingpatents for solar cell devices (molybdenum thin film as barrier layer aswell as back-end contact): U.S. Pat. No. 7,053,294 (Thin Film Solar CellFabricated on a Flexible Metallic Substrate), U.S. Pat. No. 4,915,745(Thin Film Solar Cell and Method of Making), The Fabrication and Physicsof High-efficiency CdTe Thin Film Solar Cells (by Alvin, Compaan andVictor Karpov, 2003, National Renewable Energy Lab), and Development ofCu(In, Ga)Se2 Superstrate Thin Film Solar Cells (by Franz-Josef Haug,2001, Ph.D. thesis of Swiss Federal Institute of Technology Zurich).

Generally, a solar cell can include:

A) a cover glass,

B) a top electric contact layer,

C) a transparent contact,

D) a top junction layer,

E) an absorber layer,

F) a back electric contact, and

G) a substrate.

According to the invention a thin film is made by using sputteringtarget as made by the kinetic or cold spray process as discussed above.The sputtering target is preferably a powder blending at least onepowder from the following metals: tantalum, niobium, molybdenum,aluminum, zinc, tellurium, copper or gold. The film according to theinvention can be used as a back electric contact as well as barrierlayer.

According to the invention to make a semiconductor device, a sputteringtarget is made by the kinetic or cold spray process as discussed above.The sputtering target is made by the cold spray with preferably a powderblending at least one powder from the following metals, Ta, Nb, Mo, W,Cr, Ti, Hf, and Zr. The thin film made from such target is used asbarrier layer. The use of the barrier layers are well known in the art,For example, Semiconductor Carrier film, and Semiconductor Device andLiquid Crystal Module Using The Same (U.S. Pat. No. 7,164,205), Methodsof forming an interconnect on a semiconductor substrate (U.S. Pat. No.5,612,254), Fabrication of Semiconductor device (tungsten, chromium ormolybdenum, and barrier layer) (U.S. Pat. No. 7,183,206) all disclosesemiconductor devices.

A semiconductor device with thin films made according to the inventionusing a cold spray or kinetic process include titanium, tantalumniobium, tungsten, chromium, hafnium and zirconium, and their nitrides,silicides or oxy-silicides films. These films can be used as a barrierlayer and can replace the conventional tantalum films. For example, thefollowing patents describe Ta barrier layers: Tantalum Barrier Layer forCopper Metallization (U.S. Pat. No. 6,953,742), Method of PreventingDiffusion of Copper through a Tantalum-comprising Barrier Layer (U.S.Pat. No. 6,919,275), and Method of Depositing a TaN seed Layer (U.S.Pat. No. 6,911,124).

Magnetic thin film material according to the invention is made by usingsputtering target made by kinetic or cold spray processes as discussedabove. The sputtering target is made by cold spray with preferably acomposite powder blending at least two powders from at least thefollowing metals, platinum, cobalt, nickel, chromium, iron, niobium,zirconium, born elements. This magnetic film material can be used forhard disk storage device and magnetic random access memory (MRAM) inplace of the conventional magnetic thin film material. The conventionalmagnetic thin film materials are well known in the art: For example,Magnetic Materials Structures, Devices and Methods (U.S. Pat. No.7,128,988), Method and Apparatus to Control the Formation of Layersuseful in Integrated Circuits (U.S. Pat. No. 6,669,782), MagneticRecording Medium and Method for Its Production (U.S. Pat. No.5,679,473), Magnetic Recording Medium (U.S. Pat. No. 4,202,932). HardDisk Drive are well known in the art.

Optical coatings are well known in the art: For example, the followingpatents disclose optical coatings: optical reflector for reducingradiation heat transfer to hot engine parts (U.S. Pat. No. 7,208,230),Thin layer of hafnium oxide and deposit process (U.S. Pat. No.7,192,623) Anti-reflective (AR) coating for high index gain media (U.S.Pat. No. 7,170,915). According to the invention optical coatings aremade by using the thin film according to the invention. The sputteringtarget is made by the kinetic or cold spray processes as discussedabove. The sputtering target is made from hafnium, titanium orzirconium. The oxide material is hard pressed on the sputtering target.The oxide film can be made by reactive magnetron sputtering of targetdiscussed above to replace the conventional oxide thin film sputteredfrom target made by either vacuum hot press or hot isostatic pressprocess.

Inkjet printing head (containing tantalum) are well known in the art:According to the invention an inkjet printing head is made by using thethin film according to the invention. The sputtering target is made bythe kinetic or cold spray process as discussed above. The sputteringtarget is made from tantalum or niobium. The film was made by reactivesputtering with silane and/or oxygen, which can replace thetantalum-silicon-oxygen corrosion resistance film as described in U.S.Pat. No. 6,962,407. For example, Inkjet recording head, method ofmanufacturing the same, and inkjet printer (U.S. Pat. No. 6,962,407),Print head for Ink-Jet Printing A method for Making Print Heads (U.S.Pat. No. 5,859,654).

TFT-OLED (thin-film transistor organic light-emitting diode) DeviceStructure for Flat Panel Display are well known in the art. According tothe invention a thin film is made by using sputtering target that ismade by the kinetic or cold spray processes as discussed above. Thesputtering target is made from tungsten, chromium, copper, ormolybdenum. The film as gate layer sputtered from the cold spray targetcan replace the conventional thin film layer in the TFTT-OLED. Forexample, TFT-OLED are described in U.S. Pat. No. 6,773,969.

TFT-LCD (thin-film transistor Liquid Crystal Display for Flat PanelDisplay) the liquid display crystal comprises:

A) a glass substrate,

B) a source electrode,

C) a drain electrode,

D) a gate insulator,

E) a gate electrode,

F) an amorphous-silicon, polycrystalline-silicon or single crystalsilicon layer,

G) an n-doped silicon layer,

H) a passivation layer,

I) a pixel transparent electrode,

J) a common electrode,

K) a polyimide alignment layer, and

L) a storage-capacitor electrode.

Where the gate electrode is metal such as Mo, W, Al etc.

Another schematic for TFT-LCD, they use Al gate fully-capped with Mo toavoid the hillock formation of aluminum diffusion. Normally, therequired thickness of Mo over layer to prohibit the hillock formation isabout 300 A. The molybdenum fully-capped Al film with low resistivity(about 4.08 micro ohm-cm) was successfully integrated intoamorphous-Si:H TFT fabrication with high performance. See FIG. 18.According to the invention a thin film is made by using sputteringtarget that is made by the kinetic or cold spray process as discussedabove. The sputtering target is made from molybdenum, tungsten oraluminum. The film made from the sputtering target can replace theconventional aluminum and/or molybdenum layers in the TFT-LCD.

Due to the uniformity of grain size and texture through the thickness ofthe metal sputtering targets, the films obtained from such targets haveexcellent uniformity. The cold-sprayed target is “fine-grained,non-banded with random grain orientation.

In a particular embodiment of the invention a very thin film isprovided. In this embodiment, the thin film is at least 100 Å, in somecases at least 250 Å and in other cases at least 500 Å. In thisembodiment, the thin film can be up to 5,000 Å, in some cases up to3,000 Å, in other cases up to 2,500 Å and in some situations up to 2,000Å.

In addition to metal thin films on various substrates, MOx where M ismetal (oxidation), MNx (nitridation), MSi_(X) x (silicidation), and anycombination thereof (such as MO_(x)Si_(y) etc) can also be produced byreactive sputtering or ion implantation. The metal atoms according tothe invention include, but are not limited to niobium, tantalum,tungsten, molybdenum, titanium, zirconium, chromium, vanadium,magnesium, tin, lead, aluminum, zinc, copper, rhodium, silver, gold,cobalt, iron, ruthenium, rhenium, gallium, indium, antimony, mixtures oftwo or more thereof.

Glass is not perfect with regard to a lot of applications, in particularfor architectural use. On the one hand, its low reflection in the farinfrared (room temperature radiation) causes undesired losses of thermalenergy which is needed to heat buildings in colder climate regions. Onthe other hand, its high transmission in the near infrared (solarradiation) increases the energy necessary for cooling of buildings inhot climate zones.

Architectural Glass Coating are well known in the art: For example, D.C.reactively sputtered antireflection coatings (U.S. Pat. No. 5,270,858)Multilayer anti-reflection coating using zinc oxide to provideultraviolet blocking (U.S. Pat. No. 5,147,125) Coated architecturalglass system and method (U.S. Pat. No. 3,990,784)Electrically-conductive, light-attenuating antireflection coating (U.S.Pat. No. 5,091,244). According to the invention a thin film is made byusing sputtering target that is made by the kinetic or cold sprayprocess as discussed above. The sputtering target is made from zinc.During the sputtering of the zinc target, oxygen is introduced in thechamber (such as air or oxygen) thereby forming a zinc oxide thin film.The thin film made from the sputtering target can replace theconventional zinc oxide layer in the glass coating.

Carefully designed coatings on glass nowadays can overcome all thesedrawbacks. The purpose of these coatings is to control the energytransport through the glass for more efficient heating or airconditioning. The coatings are multilayers of metals and ceramics, whoseexact compositions are tailored to specific needs. Heat reflecting socalled low emissivity coatings permit a maximum amount of daylight topass through, but then block the heat that is generated when lightstrikes an object (greenhouse effect).

The most important metal compounds for large area glass coating are, butnot limited to, SiO2, SiN4, SnO2, ZnO, Ta2O5, Nb2O5 and TiO2. These thinfilm coatings can be obtained by reactive sputtering of Si, Sn, Ta, Nband Ti metal targets. The sputtering targets are made by the kinetic orcold spray process as discussed above.

Other areas thin film according to the invention can be used arecoatings such as optical coatings. Optical coatings includes reflectiveand antireflective materials, coating that provide selectivetransmission (i.e. filters), and non-linear optical application.Examples such as TiO2 thin film and Nb2O5 thin films are reactivesputtered from Ta and Nb sputtering targets.

For automobile application, coatings that transmit 70% of visible lightand reflect 100% (or nearly) of the IR and UV, are needed to meet thegoals set by automakers.

As stated above areas for the use of thin film include magnetic thinfilm materials. The impact of thin film materials science on disk-drivestorage technology is a significant revolution, a transition fromferrite heads and particulate disks to thin film disks and heads. Thefuture generation of film disks requires high coercivity and highinduction. The thin film media must also be smooth and thinner than thepresent particulate surfaces to achieve higher recording densities.Perpendicular recording appears to be the most promising technology toachieve ultrahigh recording densities. Examples of magnetic thin filmmaterials such as alloys of Co, Cr, Ni, Fe, Nb, Zr, B and Pt for storageapplications. According to the invention a thin film is made by usingsputtering target that is made by the kinetic or cold spray processes asdiscussed above. The sputtering target is made from composite of atleast two of the following metals Co, Cr, Ni, Fe, Nb, Zr, B and Pt.

Also as stated above the thin film also include semiconductorapplications. Tantalum is sputtered in an Ar—N2 ambient to form a TaNlayer which is used as a diffusion barrier layer in between a Cu layerand a silicon substrate for semiconductor chips to ensure theinterconnections using the high conductive Cu.

The present invention therefore also relates to sputter targetscomprised of the refractory metals niobium, tantalum, tungsten,molybdenum, titanium, zirconium, chromium, vanadium, and rhenium withthe metals magnesium, tin, lead, aluminum, zinc, copper, rhodium,silver, gold, cobalt, iron, ruthenium, gallium, indium, antimony,mixtures of two or more thereof or alloys of two or more thereof oralloys with other metals which have the above mentioned properties.

Preferably targets of tungsten, molybdenum, titanium zirconium ormixtures, of two or more thereof or alloys of two or more thereof oralloys with other metals, very preferably targets of tantalum orniobium, are applied by cold or kinetic spraying to the surface of asubstrate to be coated. In said cold sprayed targets the oxygen contentof the metal is nearly unchanged compared to the oxygen content of thepowders. These cold or kinetic sprayed targets show considerably higherdensities than targets produced by plasma spraying or by vacuumspraying. Furthermore, these cold or kinetic sprayed targets can beproduced without any or with small texture, depending on powderproperties and coating parameters.

Surprisingly it has been found that with decreasing oxygen content ofthe cold or kinetic sprayed target density and other properties of thesputtered thin film layers are improved. Oxygen in the sputter targetaffects the sputtering rate, and therefore the uniformity of thin film.For metallic thin film, oxygen is undesirable at high concentration dueto its effect on the resistivity of the thin film.

We have invented a tantalum sputtering target and a means ofmanufacturing that tantalum target that has a fine uniform grainstructure of essentially less than 44 microns, that has no preferredtexture orientation as measured by electron back scattered diffraction(“EBSD”) and that displays no grain size or texture banding throughoutthe body of the target and also has a reproducible microstructure fromtarget to target. In addition we have invented a process for repairingsuch targets as well as certain hot isostatically pressed (HIPed)targets that completely reproduces the microstructure of the targetbefore repair. When used to repair other targets of inferiormicrostructure, the repaired section has the improved microstructure asif the entire target had been made with this technique. The technique isnot shape or material limited having been used to make planar, profiledand cylindrical targets and spray a range of target compositions.

Improvements on the invention include thermal treatments to improveinterparticle bonding and stress reduction of the target, as well asdesigning the materials of the target assembly to minimize the effectsof the as sprayed stresses and allow thermal treatment of the entireassembly to eliminate the disassembly step required with conventionalbacking plate materials.

Thermal Management Materials by Cold Spray Technology

The goal of these metal matrix composites is to produce a compositematerials that maintains the high thermal conductivity of the metallicelements while adding the low thermal expansion coefficient of the Mo orW to reduce differential expansion and contraction of the heat sinkrelative to the silicon chip.

Traditional, the industry has developed WCu or MoCu metal matrixcomposites from either sintered Mo or W (called “Skeleton”), followed byinfiltrated with molten Cu under temperature and pressure to create ametal matrix composite. The difficulty associated with this technique isthat it is a costly operation. The infiltration temperatures aregenerally in the range of 800 C or higher.

In addition, current WCu or MoCu composite heat sink manufacturingrequires making W block first, slicing to an appropriate size, followedby Cu infiltration. Then end users need to further slice it toappropriate thickness & dimension. Cold spray can make ultra-thin,homogeneously distributed composite directly.

Cold Spray is a much less costly operation, compared to “sintering andinfiltration” operation, as it is a direct route to fabricated partsfrom powder at temperature much below the melting points of thematerials.

The following examples were prepared:

Example 1 is a planar tantalum sputter target fabrication, testing andthin film evaluation.

Two flat plates of Ta nominally ⅛″ thick, 3.1″ in diameter were coldsprayed with tantalum powder 15-38 microns in size (Amperit #151,special grade, commercially pure (>99.95 Ta) available from H.C. StarckInc) to provide a total thickness of 0.300 inches. The gas, nitrogen inone case, helium in the other, was preheated to 600.degree. C. and usedat a stagnation pressure of 3 MPa. The powder and gas were sprayed usinga Kinetiks gun commercially available from Cold Gas Technology GmbH,Ampfing, Germany. Post spraying the disk was machined to a nominal ¼″thickness and the sputter surface was polished before sputtering. (SeeFIG. 1). The targets went through a standard burn in procedure and thenemployed to make thin films using a DC magnetron sputtering unit usingstandard conditions.

FIG. 2 shows the target surfaces post sputtering. For comparisonpurposes a standard rolled plate target was also sputtered under thesame conditions. The measured properties of the films produced are shownin the table 1 below. Table 1 shows that the films produced from thecold sprayed targets have a better uniformity, a very attractive featureto integrated circuit (“IC”) manufacturers as it allows lower filmthicknesses to be employed, and smaller circuits to be etched in lesstime with less tantalum wastage in the process. Improved uniformity isessential to both electrical and physical properties and in the questfor reduced circuitry sizes on chips. This improved uniformity resultsdirectly from the very fine and random grain structure of a cold sprayedtarget compared to a conventional target.

This improved uniformity is directly relatable back to the used targetsurfaces shown in FIG. 4. FIG. 4 illustrates close ups of a rolled ingotmetallurgy target (top) and He (helium) cold sprayed target (bottom).Post sputtering the rolled target had a mottled and irregular surface ofthe rolled target compared to the surface of the cold sprayed target.The smoother, non mottled surface of the cold spray target results fromthe more uniform non textured microstructure that in turn produces amore uniform sputtering rate and resulting film (see FIG. 3). Also shownin table one is that the Festivities and surface morphologies aresimilar for all three films. Thus, it may be concluded the cold sprayedtargets produced sputtered films as good or better than conventionaltargets made from rolled ingots. FIG. 3 also shows that the filmsproduced from the targets have different internal morphologies, with thehelium sprayed target resulting in a columnar internal structure (FIG.3A), with the helium sprayed target resulting in a equiaxed internalstructure (FIG. 3B), and with the rolled target resulting in arelatively featureless internal structure (FIG. 3C).

TABLE 1 Properties of sputtered films. Film Average ThicknessManufacture Thickness Thickness Non- Resistivity Micro Surface Film #Process (nm) (nm) uniformity Rs (Ohm/sq) (Ohm · cm) structure Morphology106 CS He 230, 168, 198 1.50% 8.642 ± 2.4% 1.71E−04 smooth 197 107 CS He157, 170, 166 3.40% 10.281 ± 3.6%  1.71E−04 columnar smooth 170 109 CSH2 288, 288, 268 3.50% 8.713 ± 3.6% 2.33E−04 smooth 227 110 CS H2 288,204, 233 4.00% 7.867 ± 4.0% 1.83E−04 equiaxed smooth 206 111 rolled4.30% 8.421 ± 4.4% 112 rolled 244 244 5.00% 7.878 ± 4.2% 1.92E−04featureless smooth 113 rolled 15.40% 4.120 ± 12%  114 rolled 275, 248,251 7.40% 6.761 ± 7.9% 1.70E−04 featureless smooth 230

Example 2 Tubular Tantalum Target Preforms Fabrication andMicrostructural Analysis

Tubular tantalum performs (see FIG. 5) were fabricated using the sameoperational parameters of example 1. Samples were cut from the preformsand annealed at different temperatures. Then metallographic mounts wereprepared and microstructural analysis performed on the as sprayed andannealed specimens. A summary of the properties is shown in Table 2. Allsamples came from a perform that used a powder having a starting mediansize of 15.9 microns (particle count based distribution) andapproximately 26 microns (mass based distribution).

TABLE 2 Summary of microstructural properties of cold sprayed tantalum,as sprayed and with a subsequent anneal. As Annealed Annealed AnnealedHIP'd Condition Deposited 942 C. 1150 C. 1450 C. 1300 C. Powder size15.9 15.9 15.9 15.9 15.9 (m) Grain Size 12   12    6.7 10.6  5.5 (m)Grain Shape Elongated Elongated Equiaxed Equiaxed Equiaxed Recrystal- NoNo Yes Yes Yes lized Crystal- Random Random Random Random Randomlographic Orientation

Table 2 and FIG. 6 reveal the characteristic features of cold sprayedtantalum in both the as sprayed, annealed and hot isostatically pressed(HIP) condition. Process temperatures are shown in the figures. Allanneals were held at temperature for 1.5 hours and the HIP cycle was attemperature for 3 hours. Starting powder size appears to control theresulting grain size, even after high temperature anneals. Thuscharacteristically the grain size of cold sprayed material is less than44 microns while even extensively worked ingot material will typicallyhave grain sizes of 60-100 microns and even larger. Again this finergrain size is an important characteristic of the target resulting inmore uniform films. However, to work it must be combined with acompletely non textured microstructure.

FIG. 6 illustrates, the flattened, or elongated or lenticular structureof the as sprayed material that recrystallizes to equiaxed grains duringanneal, the very fine grain structure both before and post anneal andthat even after extensive anneals the grain size remains equal to orsmaller than the original powder particle size.

Four cold spray and one plasma sprayed samples were examined by electronback scattered diffraction (EBSD) to determine the nature of thecrystallographic texture present. All were through-thickness samples,and all were oriented for EBSD so the spray direction was verticallydownwards.

“Texture” in the context of Materials Science means “crystallographicpreferred orientation”. A sample in which these orientations are fullyrandom is said to have no texture. If the crystallographic orientationsare not random, but have some preferred orientation, then the sample hasa weak, strong, or moderate texture. The EBSD gets orientationinformation of specimen by applying Kikuchi diffraction pattern that isformed when specimen is tiled about 70° C.

The samples were then characterized by EBSD at high resolution (2 & 4 μmstep sizes) or lower resolution (50 μm) after being mounted, polishedand etched with step size as shown in Table 3. The selection of stepsize is based on sample's grain size to ensure that small features arenot missed while completing EBSD scan at reasonable time.

TABLE 3 PROCESS EBSD STEP EBSD AREA % INDEXED CS, 1450° C. 2 μm 330 μm ×300 94 CS, 1150° C. 2 μm 330 μm × 300 95 CS, 942° C. 2 μm 280 μm × 25066 CS, No Anneal 4 μm 3 areas, 71 to 73 330 μm × 150 Plasma Spray 50 μm 2.95 mm × 9    96

Results—Cold Spray, Annealed at 1450 C

The texture maps relative to the 3 orthogonal directions are shown inFIG. 7A. Grains oriented within 20.degree. of the {100} direction aredesignated as blue, within 20° of the {111} direction yellow, and within20° of the {110} direction red, with the color getting darker as themisorientation decreases. The gray color indicated grains oriented inbetween the three orientations. The random distribution of the colors inthe figure results from the random distribution of the individualgrains. If the grains exhibited any texturing there would be apredominance of one of the colors. i.e if most of the grains wereorientated in the {100} direction yellow would be the dominant color.

The pole figures (FIG. 7B) also display a complete lack of symmetryagain indicating a lack of texture in the microstructure. It can beconcluded from the texture maps and the pole figures that the sample hasa random texture that is free of texture banding and the grains arerandom-oriented with small grain sizes and no systematic features.

Results—Cold Spray, Annealed at 1150 C

The texture was random as shown in the texture grain maps and the polefigures in FIG. 8. The grain structure was finer than that of thespecimen annealed at 1450 C.

Results—Cold Spray, Annealed at 942 C

This sample also has a random texture, as shown in FIG. 9. However, theindexing rate was much lower than for the previous specimens, indicatingthat the material retained a high strain—it had not recrystallized atthe lower annealing temperature.

Results—as Cold Sprayed (No Anneal)

Again, the texture was found to be random, and uniformly random throughthe thickness, as shown in the maps and pole figures (See FIGS. 10 &11). In this case, the 3 maps below represent the 3 areas examined, thefirst of which is of the first material deposited (the bottom of thesprayed layer), and the last of which is of the last material deposited(the top of the sprayed layer): all show the texture relative to thevertical direction (through-thickness direction to be random.

Results—Plasma-Sprayed

The base-plate or backing plate (the lower part of the maps at FIGS.12-13) had equiaxed, very large, grains, with a texture typical ofrolled and over annealed plate. The grains in the maps are mainly blueand yellow, and the pole figures H3, which include only the lowerone-third of the texture grain map, show peaks (though relatively weakpeaks) at {100}//ND and {111}//ND, where ND means the normal to thesample surface. The 3-fold symmetry of the H3 pole figures is evidenceof rolling.

The plasma deposited material shows columnar grains, with many low-angleboundaries (in red in the grain map). The texture is mainly {100}//ND,as shown in the pole figures H1 (top third of the texture grain map) andby the predominance of blue in the map. Pole figures H1 are effectivelyaxisymmetric.

The origin and cause of the even-coarser equiaxed zone below thecolumnar grains is not known.

Both H1 and H3 pole figures were made with 15° smoothing-angle halfwidth (compared to the usual 10°) to avoid introduction of extraneouspeaks, since the number of points included is very small.

In brief the above EBSD analysis shows a completely random non texturedmicrostructure in the as-cold sprayed and annealed cold sprayed targets,independent of annealing temperature. The plasma sprayed target showedsignificant texturing.

Example 3 TaNb Cold-Sprayed Target

A 50/50 w/0 NbTa rectangular target was cold sprayed directly upon acopper backing plate. FIG. 14 shows the 3 mm of bow produced in the Cuplate due to the as sprayed stresses in the deposit. Backing plates mustbe flat to seal against their mating flanges. The bow cannot be machinedout, as the stresses will simply redistribute during machining resultingin continued distortion. The bow can also not be mechanically pressedout since as sprayed Ta, TaNb and cold sprayed deposits in general havevery limited ductility (FIG. 15).

Experiments showed however, that ductility could be greatly improved byannealing. FIG. 16 shows that a Ta deposit, after annealing at 950 C for1.5 hours could be plastically deformed to take a permanent set. Thecopper backing plate was removed from the target; the target was thenannealed, bent flat and machined.

What is also apparent, from this example, is that the traditionalbacking plate materials of copper and aluminum are not ideal forrefractory metal targets by cold spray. While they have high thermalconductivities their elastic module tend to be low (encourages warpage),have a large coefficient of thermal expansion (“CTE”) mismatch with therefractory metals (encourages warpage and increases the likely hood ofbond failure between the target and backing plate during annealing) andhave low melting points (preventing annealing processes while thebacking plate is attached). Table 4 shows that materials like Mo, Ti or316 stainless steel have better combinations of properties to resistbowing during the cold spray process (high elastic modulus) or wouldallow annealing at the high temperatures required for refractory metals(CTE's close to those of the refractory metals and high melting points).

Cold spray can be used to make a multilayered target that overcomes theCTE mismatch and resulting problems described above. Instead of sprayingsputterable target material directly on the backing plate a thin coatingor coatings that have a CTE between that of the backing plate and thetarget material can be sprayed first. These intermediate layers may havea thickness of 0.25 to 2.0 mm. One way of spraying such a layer is touse a mixture of powder comprising the backing plate material and thetarget material.

TABLE 4 Target and backing plate material properties. Thermal ElasticCoefficient of Thermal Melting Conductivity Modulus Expansion PointMaterial Cal cm/cm²sec C. ×10⁻⁶ PSI cm/cm C. C. Cu 0.94 17 16.5 1083 Al0.53 10 23.6 660 Nb 0.12 17 7.3 2468 Ta 0.13 27 6.5 2996 Mo .34 47 4.92610 Ti 0.22 16.8 8.4 1668 316 SS 28 14 ~1350

Example 4 Sputtering of Cold Sprayed NbTa Target

The pseudo-alloy (the Ta and Nb powders remain chemically distinct)target was placed in a 1 8″×5″ planar magnetron cathode sputterer.Target dimensions were 4″×17″×approx. 0.125″.

Three tests were conducted: straight metal deposition, oxide depositionand nitride deposition. The conditions used and results obtained aredescribed below.

Straight Metal Deposition

Sputtering was conducted using argon gas at 100 sccm with a sputteringpressure of 1.0.times.1 0-3 torr (base pressure 4.times.10-5 torr), 5.0kilowatts, 550 volts, roughly 73 watts/in.sup.2. Target sputtered verynicely right from the beginning. No arcing, no real “burn in” timeneeded for stability.

A final film thickness of 1401 angstroms was deposited on a glass slide(as measured by a Dektak 2A microprofilometer). This is a rate of 1angstrom/(watt/in²)/second of deposition time, slightly higher than theindividual rates for Nb and Ta. Film resistance of 3.7 ohm/sq. (asmeasured on the glass slide with a 4 pt. Probe). This works out to be51.8□-ohm cm.

That is higher than the expected resistivity of approx. 28□-ohm cm. Thismaterial is sensitive to background pressure (impurities) and pumping tothe low-5 to -6 torr range may be necessary for appropriate resistivitynumbers. Solar absorption of the film is 0.41 (as measured andcalculated per ASTM 5903 and E490).

Oxide Deposition.

Sputtering was conducted using argon at 100 sccm and oxygen at 90 sccm(lower oxygen levels resulted in gradually switching to metal mode) at1.2-3 torr. 3.0 Kilowatts (44 watts/in2) at 680 volts. This is one ofthe few materials that has a higher sputtering voltage in oxide modethan in metal mode. Using the MDX D.C. supply with an add on Sparc-leunit operating at 20 KHz. again yielded a very stable sputtering processwith no arcing and no problems. Sputtering yield was 40% of metal rate.This process gave a very nice looking transparent film with a slightpink tint in transmission and a slight green tint in reflection. Finalfilm thickness was 4282 angstroms. Calculated index of refraction is2.8. This is higher than the index for the individual tantalum andniobium oxides (approx. 2.2 to 2.3).

Nitride Deposition.

Sputtering was conducted using argon at 100 sccm and nitrogen at 200sccm, approx. 2.0×10-3 torr sputtering pressure. The nitride sputterednicely and was quite stable. However, even after trying many processparameters and were unable to produce a transparent nitride coating. 3.0kilowatts with the MDX and Sparc-le unit worked well. Sputtering yieldwas 51% of metal rate. Final film thickness was 1828 angstroms at 69ohm/sq. (1260 micron-ohm cm). Solar absorption was measured as 0.59.

Some of the observed results were.

Sputters very nicely in metal mode.

In oxide mode, sputters very well.

No arcing noted, this means that oxide content in the target was stableand the target was not building a dielectric layer during deposition.Very high index oxide, which will be quantified and measurements forvariations as a function of chemistry due to position and time.

Quite well defined race track, no discoloration in the race track.

Overall target deposits at a good rate.

Target was run at a peak power of 5 kW which translates into 75watts/sq.in.—for reference Ti or Ni—Cr is sputtered at 35 watts/sq.in.

Target power was ramped up in 1 kW increments, no problems were noted.

At high power, no problems were noted in terms of target expansion,excessive heating.

Good dimensional stability, no problems at the clamps or edges.

Example 5

Annealing and flattening of a cold sprayed TaNb target on a copperbacking plate. A 17″ by 1.5″ by 0.300 TaNb deposit was cold sprayed on a0.500 thick Cu backing plate. Prior to spraying the pure TaNb a 50% Cu50% (TaNb) layer approximately 0.030″ thick was sprayed on the Cu toprovide an intermediate compliant CTE layer. The as sprayed assembly hada mid point bow of approximately 0.2 inches. The target assembly wasthen vacuum annealed at 825 C for 1.5 hours just sufficient to introducerecovery in the niobium and make it ductile. Upon cooling the targetassembly was placed in a press, successfully pressed flat to within0.010″ and finish machined.

Example 6

MoTi sputtering targets of approximately 50/50 a/o composition wheremade by Hot Isostatic Pressing (HIP) and by cold spraying. The MoTialloy system does not exhibit 100% solid solubility and contains severaldeleterious brittle intermediate phases. When Mo and Ti are alloyed inthe liquid state these phases are unavoidable. A goal in developing HIPparameters is to minimize the formation of these phases, But due tointerdiffusion of the two elements again they are unavoidable if fulldensity is to be achieved. FIG. 23 clearly shows the presence of thesedeleterious phases in powders that were HIP'ed at 825 C, 15,000 ksi for7 hours. An approximately 15-20 micron thick zone of third phasematerial surrounds both the titanium and the molybdenum powders 24,however, shows that there is no interdiffusion of the Mo and Ti and thatonly pure elemental Mo and pure elemental Ti phases exist in the targetproduced by cold spray. FIG. 25 shows that even after a 1.5 hour annealat 700 C substantially no interdiffusion, and no visable, at thismagnification, deleterious phases have formed.

The Cold Spray Conditions for Making Tungsten-Copper (WCu) CompositeThermal Management Materials are Listed Below:

Equipment: Cold Gas Technology GmbH (Germany) Kinetiks 3000 or Kinetiks4000

Cold Spray Conditions: Nitrogen atmosphere at 600-900 C and pressure at2.0-4.0 MPa, powder feeding rate at 30-90 g/min, and spray distance10-80 mm.

Preferred conditions: 800-900 C and pressure 3-3.8 MPa, powder feedingrate 30-50 g/min and spray distance 20-40 mm.

Powders Used:

Tungsten (W): AMPERIT® 140, 25/10 μm particle size cut, sintered, andCopper (Cu): AMPERIT® 190, 35/15 μm, gas atomized. Both materials aremade by H.C. Starck GmbH. The cold-sprayed WCu samples were made bymixing about 50% vol of W and 50% of Cu and fed through the powderfeeder of CGS Cold Spray System to make WCu composite. The substratescan be either stainless steel or titanium. The bonding between compositestructure and substrate is excellent. The microstructure of W—Cu (50/50vol %) is shown in FIGS. 26A and 26B.

The table below showed that the as-spray WCu has thermal conductivity of193 W/m-K, and thermal expansion coefficient of 13.49 ppm/degree C.Annealing at 1600 F (871 C) for 2 hrs and 4 hrs showed significantimprovement for both thermal conductivity and coefficient of thermalexpansion. It clearly demonstrated that annealing is an important stepto significantly enhance the thermal conductivity and to lower thethermal expansion coefficient for cold spray thermal managementmaterials.

Thermal Conductivity Coefficient of Thermal Sample ID W/m · K Expansionppm/C. As-is 193 13.49  2 hr × 1600 F. 281 11.8 4 hrs × 1600 F. 27611.82

The thermal management products made by cold spray technology have thefollowing composition

WCu composite: with W content varying from 10% to 85%

MoCu composite; with Mo content varying from 10% to 85%.

The major features of composites made by cold spray process for thermalmanagement application are:

(a) Cu—flattened microstructure, others materials such as: Ag, Al or Aucan also be used.

(b) Mo or W will maintain substantially its particle morphology oragglomerated particles. Other materials such as Aluminium nitride (AlN),silicon carbide (SiC) can also be used. The microstructure of W—Cu(50/50 vol %) is shown in FIGS. 26 A and B.

All the references described above are incorporated by reference in itsentirety for all useful purposes.

While there is shown and described certain specific structures embodyingthe invention, it will be manifest to those skilled in the art thatvarious modifications and rearrangements of the parts may be madewithout departing from the spirit and scope of the underlying inventiveconcept and that the same is not limited to the particular forms hereinshown and described.

We claim:
 1. A method of rejuvenating a sputtering target, the methodcomprising: providing a sputtering target initially formed by ingotmetallurgy or powder metallurgy and comprising a sputtering-targetmaterial, the sputtering-target material (i) comprising a refractorymetal, (ii) defining a recessed furrow therein, and (iii) having a firstgrain size and a first crystalline microstructure; and spray-depositinga powder within the furrow to form a layer therein, the layer (i)comprising the metal, (ii) having a second grain size finer than thefirst grain size, and (iii) having a second crystalline microstructuremore random than the first crystalline microstructure, whereinspray-depositing the powder within the furrow forms a distinct boundaryline between the layer and the sputtering-target material.
 2. The methodof claim 1, wherein the sputtering target comprises a backing plate uponwhich the sputtering-target material is disposed.
 3. The method of claim2, wherein the powder is spray deposited without removal of the backingplate from the sputtering-target material.
 4. The method of claim 1,wherein spray-depositing the powder comprises cold spray.
 5. The methodof claim 1, wherein the refractory metal is selected from the groupconsisting of niobium, tantalum, tungsten, molybdenum, zirconium,titanium, and alloys thereof.
 6. The method of claim 1, wherein thelayer has a uniformly random texture.
 7. The method of claim 1, whereinthe second grain size is less than 44 microns.
 8. The method of claim 1,wherein the second grain size is less than 10 microns.
 9. The method ofclaim 1, wherein the layer is substantially free of grain-size bandingand texture banding.
 10. The method of claim 1, further comprising,after spray-depositing the powder, annealing the sputtering target. 11.The method of claim 1, further comprising, after spray-depositing thepowder, at least one of grinding or polishing a surface of the layer.12. The method of claim 1, wherein spray-depositing the powder comprisesspray-depositing the powder only in the furrow.
 13. The method of claim1, wherein spray-depositing the powder comprises spray-depositing thepowder in the furrow and on the sputtering-target material outside ofthe furrow.
 14. The method of claim 1, wherein the sputtering-targetmaterial comprises regions of different preferred crystallineorientations, and the layer substantially lacks a preferred crystallineorientation.
 15. The method of claim 1, further comprising, afterspray-depositing the powder, diffusion bonding the layer to thesputtering-target material.